With the rapid expansion of market of notebook computers, cellular phones, electric vehicles, and the like, there is a need for a secondary battery having high energy density. Examples of the means for obtaining a secondary battery having high energy density include a method in which a negative electrode material having a large capacity is used, and a method in which a non-aqueous electrolyte with excellent stability is used.
Patent Literature 1 discloses a secondary battery comprising a lithium-containing silicon oxide or silicate as a negative electrode active material. Patent Literature 2 discloses a negative electrode for a secondary battery comprising an active material layer comprising a particle of a carbon material capable of intercalating/deintercalating lithium ions, a particle of a metal capable of being alloyed with lithium, and a particle of an oxide capable of intercalating/deintercalating lithium ions. Patent Literature 3 discloses a negative electrode material for a secondary battery, wherein a surface of a particle having a structure in which microcrystalline silicon is dispersed in a silicon compound is coated with carbon. Moreover, Patent Literature 4 discloses a technique for doping a silicon-silicon oxide composite, which is coated with carbon, with lithium.
Patent Literature 5 and Patent Literature 6 disclose that a thermosetting resin which undergoes dehydration/condensation reaction by heating, or polyimide is used as a negative electrode binder when a negative electrode active material contains silicon.
Patent Literature 7 proposes a non-aqueous electrolyte comprising a trialkyl phosphate, more specifically, trimethyl phosphate, triethyl phosphate, or the like. Patent Literature 8 discloses a secondary battery, wherein a negative electrode is formed by binding a negative electrode active material, which comprises a carbon material capable of intercalating/deintercalating lithium ions, a metal capable of being alloyed with lithium, and a metal oxide capable of intercalating/deintercalating lithium ions, to a negative electrode current collector with a negative electrode binder; and an electrolyte comprises a liquid medium such as a phosphate ester compound and a fluorinated phosphate ester compound, which hardly forms carbon dioxide, in a concentration of 10 to 80 vol %.
Meanwhile, Patent Literature 9 discloses a non-aqueous electrolyte for a secondary battery, comprising a phosphate ester compound and a halogen-containing cyclic carbonate ester, and discloses that the volume ratio of the halogen-containing cyclic carbonate ester to the phosphate ester is preferably within a range of 10:1 to 1:2 (i.e., the amount of the halogen-containing cyclic carbonate ester is approximately 90.9 to 33.3 vol %, and the amount of the phosphate ester is approximately 9.1 to 66.7 vol %).